Measuring signal strength in a multiple-input multiple-output antenna environment

ABSTRACT

A wireless communication device is operated in a M by N multiple-input multiple-output (MIMO) mode. M is the number of antennas transmitting to the communication device from a first base station. N the number of receiving antennas and receivers. M and N are integers greater than one. The wireless communication device is operated in an M by N-1 MIMO mode while a first one of the N receiving antennas and a first one of the N receivers receives wireless communication from a second base station.

This application is a division of application Ser. No. 12/197,745, filedAug. 25, 2008 now U.S. Pat. No. 8,170,618 (currently in condition forallowance), and is related to application Ser. No. 13/435,031, both ofwhich are hereby incorporated by reference which is hereby incorporatedby reference.

TECHNICAL BACKGROUND

Wireless communication may be used as a means of accessing a network.Wireless communication has certain advantages over wired communicationsfor accessing a network. One of those advantages is a lower cost ofinfrastructure to provide access to many separate locations or addressescompared to wired communications. This is the so-called “last mile”problem. Another advantage is mobility. Wireless communication devices,such as cell phones, are not tied by wires to a fixed location. To usewireless communication to access a network, a customer needs to have atleast one transceiver in active communication with another transceiverthat is connected to the network.

To facilitate wireless communications, the Institute of Electrical andElectronics Engineers (IEEE) has promulgated a number of wirelessstandards. These include the 802.11 (WiFi) standards and the 802.16(WiMAX) standards. Likewise, the International Telecommunication Union(ITU) has promulgated standards to facilitate wireless communications.This includes TIA-856, which is also known as Evolution-Data Optimized(EV-DO). The European Telecommunications Standards Institute (ETSI) hasalso promulgated a standard known as long term evolution (LTE).Additional standards such as the fourth generation communication system(4G) are also being pursued. These standards pursue the aim of providinga comprehensive IP solution where voice, data, and streamed multimediacan be given to users on an “anytime, anywhere” basis. These standardsalso aim to provide higher data rates than previous generations. All ofthese standards may include specifications for various aspects ofwireless communication with a network. These aspects include processesfor registering on the network, carrier modulation, frequency bands ofoperation, and message formats.

OVERVIEW

A method of operating a wireless communication device is disclosed. Thewireless communication device is operated in a M by N multiple-inputmultiple-output (MIMO) mode. M is the number of antennas transmitting tothe communication device from a first base station. N the number ofreceiving antennas and receivers. M is an integer greater than zero. Nis an integer greater than one. The wireless communication device isoperated in an M by N-1 MIMO mode while a first one of the N receivingantennas and a first one of the N receivers receives wirelesscommunication from a second base station.

A data stream is received from a first base station using M by N MIMO. Mis a number of antennas transmitting the data stream to thecommunication device from the first base station. N is the number ofreceiving antennas and receivers receiving the data stream. M and N areintegers greater than one. The data stream is received from the firstbase station using M by N-P MIMO. P is an integer greater than zero. Anindicator of a signal strength of a second base station as measured byat least one of the N receivers is reported to the first base station.The signal strength of the second base station is measured while thewireless communication device is receiving the data stream using M byN-P MIMO.

A wireless communication device is disclosed. N antennas and N receiversare configured to receive signals from at least one base stationtransmitting signals from M antennas. The wireless communication devicereceives a first data stream based on the received signals using M by NMIMO. The wireless communication device receives a second data streamfrom the first base station using M-Q by N-P MIMO. P is an integergreater than zero. Q is an integer greater than or equal to zero. Anindicator of a signal strength of a second base station is measured byat least one of the N receivers while the wireless communication deviceis receiving the second data stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a multiple-input multiple-outputwireless communication system.

FIG. 2 is a flowchart illustrating a method of operating a wirelesscommunication device.

FIG. 3 is a flowchart illustrating a method of operating a wirelesscommunication device.

FIG. 4 is a flowchart illustrating a method of operating a wirelesscommunication device.

FIG. 5 is a block diagram of a computer system.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating a multiple-input multiple-outputwireless communication system. In FIG. 1, communication system 100comprises: base station 110, base station 120, and wireless device 130.Base station 110 includes multiple transmitters. These transmitters arerepresented in FIG. 1 by transmitter 111 and transmitter 112. Basestation 110 includes multiple antennas. These antennas are representedin FIG. 1 by antenna 115 and antenna 116. Antenna 115 and antenna 116are associated with transmitter 111 and transmitter 112, respectively.

Wireless device 130 may be any device, system, combination of devices,or other such communication platform capable of communicating with basestation 110 using multiple receivers 131 and 132 and multiple antennas135 and 136, respectively. Wireless device 130 may use communicationaspects specified by the WiMAX specification including, but not limitedto, the MIMO modes detailed therein. Wireless device 130 may be, orcomprise, for example, a mobile phone, a wireless phone, a wirelessmodem, a personal digital assistant (PDA), a voice over internetprotocol (VoIP) phone, a voice over packet (VOP) phone, or a soft phone,as well as other types of devices or systems that can exchange data withbase station 110 via multiple antennas 135 and 136. Other types ofcommunication platforms are possible.

Base station 110 may be any wireless system that provides the airinterface to wireless device 130 using multiple antennas 115 and 116.Base station 110 may also use one or more transmitters 111 and 112. Basestation 120 may be any wireless system that can provide an air interfaceto wireless device 130. Base station 110 and base station 120 may usecommunication aspects specified by the WiMAX specification including,but not limited to, the MIMO modes detailed therein. Examples of basestations that may be utilized include, base transceiver stations (BTSs),radio base stations (RBSs), Node B, enhanced Node B (eNBs) and others.Base stations may include a number of elements known to those skilled inthe art comprising transceivers, power amplifiers, combiner, duplexer,antennas and control function.

Base station 120 includes at least transmitter 121. Transmitter 121 isassociated with antenna 125. Base station 120 may include at leastadditional transmitters and antennas. Base station 120 may also includeother additional components. However, these additional components havebeen omitted from FIG. 1 for the sake of brevity.

Wireless device 130 includes multiple antennas. Wireless device 130 mayinclude one or more receivers. These receivers are represented in FIG. 1by receiver 131 and receiver 132. The antennas are represented in FIG. 1by antenna 135 and antenna 136. In FIG. 1, antenna 135 and antenna 136are associated with receiver 131 and receiver 132, respectively.

In an embodiment, wireless device 130 is operated in an M by Nmultiple-input multiple-output (MIMO) mode. M is the number oftransmitters 111 and 112 and/or antennas 115 and 116 that base station110 is using to transmit a data stream to wireless device 130. N is thenumber of receivers 131 and 132 and/or antennas 135 and 136 thatwireless device 130 is using to receive the data stream from basestation 110. In an embodiment, M and N may both be two (2). Thus,communication system 100 would be said to be operating in 2×2 MIMO mode.In another embodiment, M=1 and N=2. Thus, communication system 100 wouldbe said to be operating in 1×2 MIMO mode.

In addition to MIMO modes that specify the number of transmitting andreceiving antennas, there are MIMO modes that specify how the datastream is transmitted from the multiple transmitting antennas. A firstMIMO mode splits a data stream into multiple lower rate data streams andeach data stream is transmitted from a different transmit antenna 115 or116 in the same frequency channel. This mode may be referred to asspatial-multiplexing MIMO (SM-MIMO).

A second MIMO mode transmits multiple redundant copies of a single datastream. The single stream is coded using techniques called space-timecoding. The single stream is emitted from each of the transmit antennas115 and 116 using certain principles of full or near orthogonal coding.This mode may be referred to as diversity coding MIMO or space-timecoding MIMO (STC-MIMO).

In an embodiment, base station 110 and wireless device 130 may beoperating in an M by N MIMO mode using SM-MIMO. This means that wirelessdevice 130 is receiving M streams of data on a single frequency channel.Wireless device 130 may send a request to base station 110 to switchwireless device 130 from SM-MIMO to STC-MIMO. Wireless device 130 maythen receive from base station 110 a control message. This controlmessage may switch wireless device 130 from SM-MIMO to STC-MIMO. Thus,wireless device 130 will begin to receive a single stream of data on asingle frequency channel.

In an embodiment, wireless device 130 may determine that it needs tostart scanning. Scanning is a process whereby wireless device 130listens for signals from a second base station 120 while it is stillbeing serviced by a first base station 110. Wireless device 130 thenreports this measurement back to the first base station 130. When thestrength of the signal from the second base station 120 exceeds thesignal strength of the first base station 110, communication system 100may hand wireless device 130 over to base station 120. Criteria inaddition to or as an alternative to signal strength may be utilized toinitiate a hand-off from one base station to another base station.

In an embodiment, wireless device 130 is operating in M by N STC-MIMOmode. Wireless device 130 switches to operating in M by N-1 STC-MIMOmode. Wireless device 130 then uses the now extra antenna and receiverfor the scanning process.

For example, consider the case where wireless device 130 and basestation 110 are operating in 2 by 2 STC-MIMO mode. Thus, transmitters111 and 112 are both transmitting the same data stream (although withdifferent encodings) via antennas 115 and 116, respectively. Wirelessdevice 130 is receiving the data stream using receivers 131 and 132 viaantennas 135 and 136, respectively.

Wireless device 130 may switch to operating in 2 by 1 STC-MIMO mode.Thus, wireless device 130 is receiving the data stream using onlyreceiver 131 and antenna 135. This allows wireless device 130 to usereceiver 132 and antenna 136 for scanning. For example, wireless device130 may use receiver 132 and antenna 136 to measure a signal strengthtransmitted from base station 120 via transmitter 121 and antenna 125.An indicator of the signal strength may be reported back to base station110. Based on this indicator of signal strength, communication system100 may determine that wireless device 130 is to be handed-off to basestation 120.

By switching from M by N MIMO to M by N-1 MIMO, wireless device 130 isable to perform the scanning process without disconnecting from basestation 110. This helps prevent data traffic from being interruptedduring the scanning process. Interrupting data traffic during thescanning process may adversely affect certain communication protocols.For example, interrupting TCP packet flow can trigger the TCP congestionavoidance algorithm. This may result in a reduction of data rate by halfor more. In another example, interrupting data traffic associated with avoice over IP (VoIP) flow can increase latency and jitter. This degradesthe user experience.

FIG. 2 is a flowchart illustrating a method of operating a wirelesscommunication device. The steps illustrated in FIG. 2 may be performedby one or more elements of communication system 100.

A wireless communication device is operated in M by N MIMO mode (202).For example, wireless device 130 may be operated in M by N MIMO mode. Inanother example, wireless device 130 may be operated in 2 by 2 MIMOmode.

The mode of the wireless communication device is changed to operate in Mby N-1 MIMO mode (204). For example, the mode of wireless device 130 maybe changed to operate in M by N-1 MIMO mode. In another example, themode of wireless device 130 may be changed to operate in 2 by 1 MIMOmode.

Communication from a second base station is received using an availablereceiver and antenna (206). For example, wireless device 130 may receivecommunication from base station 120 using an available receiver 132 andantenna 136. In an example, the available receiver 132 and antenna 136may be the Nth receiver and antenna that were in use before the switchto M by N-1 MIMO mode. In another example, wireless device 130 maymeasure, using an available receiver 132 and antenna 136, the signalstrength of the received communication from base station 120. In anotherexample, an indicator of the signal strength of the receivecommunication may be reported to one or more elements of communicationsystem 100.

FIG. 3 is a flowchart illustrating a method of operating a wirelesscommunication device. The steps illustrated in FIG. 3 may be performedby one or more elements of communication system 100.

A data stream is received from a first base station using M by N MIMO(302). For example, wireless device 130 may receive a data stream frombase station 110 using M by N MIMO. In another example, wireless device130 may receive a data stream from base station 110 using 2 by 2 MIMO.In another example, wireless device 130 may receive a data stream frombase station 110 using 2 by 2 MIMO as given in the WiMAX specification.

A data stream is received from the first base station using M by N-PMIMO (304). P is an integer greater than zero. For example, if P=2,wireless device 130 may receive a data stream from base station 110using M by N-2 MIMO. In another example, wireless device 130 may receivea data stream from base station 110 using 2 by 1 MIMO. In anotherexample, wireless device 130 may receive a data stream from base station110 using 2 by 1 MIMO as given in the WiMAX specification.

While receiving a data stream from the first base station using M by N-PMIMO, a signal strength of a second base station is measured (306). Forexample, while wireless device 130 receives a data stream from basestation 110 using M by N-2 MIMO, wireless device 130 may measure asignal strength of base station 120. In another example, while wirelessdevice 130 receives a data stream from base station 110 using 2 by 1MIMO, wireless device 130 may measure a signal strength of base station120 using the receiver and antenna that were formerly used in whenwireless device 130 was in 2 by 2 MIMO.

An indicator of signal strength is reported (308). For example, wirelessdevice 130 may report to base station 110 an indicator of the signalstrength associated with base station 120. In another example, wirelessdevice 130 may report to base station 120 an indicator of the signalstrength that it is experiencing from base station 120.

FIG. 4 is a flowchart illustrating a method of operating a wirelesscommunication device. The steps illustrated in FIG. 4 may be performedby one or more elements of communication system 100.

A first data stream is received from a first base station using M by NMIMO and spatial multiplexing (402). For example, wireless device 130may receive a first data stream from base station 110 using M by N MIMOand spatial multiplexing. In another example, wireless device 130 mayreceive a first data stream from base station 110 using 2 by 2 MIMO andspatial multiplexing. In another example, wireless device 130 mayreceive a first data stream from base station 110 using 2 by 2 MIMO andspatial multiplexing as given in the WiMAX specification.

A request to switch to diversity coding and M-Q by N-P MIMO is sent tothe first base station (404). Q is an integer greater than or equal tozero. For example, wireless device 130 may send a request to basestation 110 to switch to diversity coding scheme (such as space-timecoding) and M-Q by N-P MIMO. In another example, wireless device 130 maysend a request to base station 110 to switch to diversity coding and M-1by N-1 MIMO. In another example, wireless device 130 may send a requestto base station 110 to switch to diversity coding and 2 by 1 MIMO.

A control message to switch to diversity coding and M-Q by N-P MIMO isreceived from the first base station (406). For example, wireless device130 may receive a control message from base station 110 to switch todiversity coding and M-Q by N-P MIMO. In another example, wirelessdevice 130 may receive a control message from base station 110 to switchto diversity coding and M-1 by N-1 MIMO. In another example, wirelessdevice 130 may receive a control message from base station 110 to switchto diversity coding and 2 by 1 MIMO.

A signal strength of a second base station is measured using at leastone of the N receivers (410). For example, wireless device 130 maymeasure a signal strength of base station 120 using at least one ofreceiver 131 and receiver 132. In another example, wireless device 130may measure a signal strength of base station 120 using multiplereceivers. In an embodiment, if P is greater than or equal to 2, asignal strength of a base station transmitting in a MIMO mode may bemeasured by multiple receivers (and antennas). Thus, a MIMO signalstrength of the second base station may be measured. For example, ifwireless device 130 had at least three receivers (and antennas), andbase station 120 was transmitting with at least two transmitters (andantennas), then wireless device 130 could measure the signal strength ofbase station 120 in 2 by 2 MIMO mode while still communicating with basestation 110 in 2 by 1 MIMO mode.

A signal strength report is sent (412). For example, wireless device 130may send a signal strength report associated with base station 120 tobase station 110. In another example, wireless device 130 send a signalstrength report to base station 120 indicating of the signal strengththat it is experiencing from base station 120.

The methods, systems, transmitter, receivers, and base stationsdescribed above may be implemented with, contain, or be executed by oneor more computer systems. The methods described above may also be storedon a computer readable medium. Many of the elements of communicationsystem 100 may be, comprise, or include computers systems. Thisincludes, but is not limited to: communication system 100, base station110, base station 120, and wireless device 130.

FIG. 5 illustrates a block diagram of a computer system. Computer system500 includes communication interface 520, processing system 530, anduser interface 560. Processing system 530 includes storage system 540.Storage system 540 stores software 550. Processing system 530 is linkedto communication interface 520 and user interface 560. Computer system500 could be comprised of a programmed general-purpose computer,although those skilled in the art will appreciate that programmable orspecial purpose circuitry and equipment may be used. Computer system 500may be distributed among multiple devices that together compriseelements 520-560.

Communication interface 520 could comprise a network interface, modem,port, transceiver, or some other communication device. Communicationinterface 520 may be distributed among multiple communication devices.Processing system 530 could comprise a computer microprocessor, logiccircuit, or some other processing device. Processing system 530 may bedistributed among multiple processing devices. User interface 560 couldcomprise a keyboard, mouse, voice recognition interface, microphone andspeakers, graphical display, touch screen, or some other type of userdevice. User interface 560 may be distributed among multiple userdevices. Storage system 540 could comprise a disk, tape, integratedcircuit, server, or some other memory device. Storage system 540 may bedistributed among multiple memory devices.

Processing system 530 retrieves and executes software 550 from storagesystem 540. Software 550 may comprise an operating system, utilities,drivers, networking software, and other software typically loaded onto acomputer system. Software 550 could comprise an application program,firmware, or some other form of machine-readable processinginstructions. When executed by processing system 530, software 550directs processing system 530 to operate as described herein.

The above description and associated figures teach the best mode of theinvention. The following claims specify the scope of the invention. Notethat some aspects of the best mode may not fall within the scope of theinvention as specified by the claims. Those skilled in the art willappreciate that the features described above can be combined in variousways to form multiple variations of the invention. As a result, theinvention is not limited to the specific embodiments described above,but only by the following claims and their equivalents.

What is claimed is:
 1. A method of operating a wireless communicationdevice, comprising: receiving a data stream from a first base stationusing M by N MIMO, wherein M is a number of antennas transmitting thedata stream to the communication device from the first base station, andwherein N is a number of receiving antennas and receivers receiving thedata stream, and wherein M and N are integers greater than one;receiving the data stream from the first base station using M by N-PMIMO, wherein P is an integer greater than zero; and, reporting anindicator of a signal strength of a second base station as measured byat least one of the N receivers to the first base station, wherein thesignal strength of the second base station is measured while thewireless communication device is receiving the data stream using M byN-P MIMO.
 2. The method of claim 1, wherein M=2, N=2, and P=1.
 3. Themethod of claim 1, wherein the wireless communication device usesspace-time coding MIMO when using M by N-P MIMO.
 4. The method of claim1, wherein the wireless communication device uses spatial multiplexingMIMO when using M by N MIMO and makes a change to space-time coding MIMOwhen using M by N-P MIMO.
 5. The method of claim 4, further comprising:receiving a control message from the first base station to change thewireless communication device from spatial multiplexing MIMO tospace-time coding MIMO.
 6. The method of claim 4, further comprising:sending a request message to the first base station to change fromspatial multiplexing and M by N MIMO to space-time coding and M by N-PMIMO.
 7. The method of claim 6, wherein the wireless communicationdevice begins scanning after the change to space-time coding and M byN-P MIMO.
 8. A wireless communication device, comprising: N antennas andN receivers configured to receive signals from at least one base stationtransmitting signals from M antennas; wherein the wireless communicationdevice receives a first data stream based on the received signals usingM by N MIMO; and wherein the wireless communication device receives asecond data stream from the first base station using M-Q by N-P MIMO,wherein P is an integer greater than zero and Q is an integer greaterthan or equal to zero; and, wherein an indicator of a signal strength ofa second base station is measured by at least one of the N receiverswhile the wireless communication device is receiving the second datastream.
 9. The wireless communication device of claim 8, wherein M=2,N=2, P=1, and Q=0.
 10. The wireless communication device of claim 8,wherein the wireless communication device uses space-time coding MIMOwhen using M-Q by N-P MIMO.
 11. The wireless communication device ofclaim 8, wherein Q=P, and wherein the wireless communication device usesspatial multiplexing MIMO when using M by N MIMO, and wherein thewireless communication device uses spatial multiplexing MIMO when usingM-Q by N-P MIMO.
 12. The wireless communication device of claim 11,wherein the wireless communication device sends a request to the firstbase station to change from M by N MIMO to M-Q by N-P MIMO.